[raster] ST_DumpAsPolygons() stop differenciate values when they are higher than 1048576

[pracine]

This works fine:

SELECT (ST_DumpAsPolygons(ST_SetValue(ST_AddBand(ST_MakeEmptyRaster(1, 2, 0, 0, 1), '32BUI'::text, 1048575), 1, 1, 1048576))).* rast

returning two polygons, but this fails:

SELECT (ST_DumpAsPolygons(ST_SetValue(ST_AddBand(ST_MakeEmptyRaster(1, 2, 0, 0, 1), '32BUI'::text, 1048576), 1, 1, 1048577))).* rast

The only difference is when the pixel values get over 1048576 (which is 0x10000 by the way).